In the early days of hearing device technology the hearing devices merely served as simple sound amplifiers. Since with a hearing impairment not all frequencies are typically equally affected, with some frequencies thus being able to be perceived better than others, frequency-dependent amplification is necessary to compensate for the hearing impairment in the optimum way. Only by the use of filter circuits could the transmission characteristics of the hearing device, i.e. the manner in which an audio signal is modified by the components of the hearing device, be individually adapted to the extent where a realistic hearing impression was possible. The filter circuits realized initially with the aid of analog technology have become ever more mature during the course of development, with the increasing complexity of these circuits also resulting in a plurality of adjustment and control options. In newer designs of hearing device the signal processing of the audio signal received from the hearing device microphone may thus be adapted so that it meets the individual requirements of the respective hearing device wearer. The adaptation of the hearing device aims to optimize the settings of the hearing device and this procedure is generally undertaken by a hearing device acoustic technician.
A significant advantage of analog technology is that the signals are processed in real time. However settings can only be made on analog signal processing circuits to a limited extent as a result of the small size of the hearing device. The noise typical of analog signal processing also represents a not insignificant problem. The disadvantages of analog technology could not be avoided until the advent of digital signal processing circuits in hearing device technology. Programmable hearing devices basically open up new degrees of freedom in defining the functionality of a hearing device. The type of signal processing in this case is fully freely definable and can be executed in the form of programs in the hearing device. Only the development of digital programmable hearing devices thus made it possible to provide a number of alternate hearing programs which are intended for example to provide optimum perception of speech when confronted with various noise barriers.
The hearing devices on the market essentially feature the same basic components. In addition to a microphone, a signal processing device and an electroacoustic converter, generally a loudspeaker, modern hearing devices also have a programmable control device which controls the signal processing device, to set the transmission characteristics of the hearing device to individual requirements. The control device is preferably programmed in this case with the aid of data obtained audiometrically.
Since the hearing device does not as rule have a complex adjuster because of the small size of its housing, it has to be programmed in a programming session with the aid of an external control device. Real everyday situations are simulated during the programming. Different audio samples can be copied into the hearing device via the control device for this purpose, which, after signal processing in the hearing device, are qualitatively assessed by the hearing aid wearer. This feedback allows the acoustic technician to manually set individual parameters during fine tuning. Typically the control device or an external adaptation computer connected to the control device features corresponding input devices for this purpose. The adaptation of the hearing device is preferably undertaken here in a number of stages. Preprogramming can thus initially be undertaken on the basis of audiometrically determined parameters and the hearing device can then be fine tuned.
During fine tuning it is necessary to transmit audio signals with the optimum possible quality to the hearing device. Thus the hearing device is conventionally connected to the programming device for programming via a special audio cable. Since in such cases complex tine sequences and noises sometimes have to be created or analyzed, the programming of the hearing device requires a comparatively large amount of computing power. It is thus advantageous to use an external adaptation computer for programming which is connected to the control device. Such an adaptation computer generally features an operator keyboard, via which the hearing device acoustic technician can make the corresponding settings. The control device does not need any processing power of its own in this case. Instead it can then be embodied as a simple remote control, which merely forwards the data of the adaptation computer to the hearing device. Such a remote control can however also contain closed-loop controllers for specific setting of the hearing device, such as the absolute volume for example. Furthermore the remote control can feature a separate tone generator which creates audio signals from data calculated by the adaptation computer and transferred to the control device. These audio signals only then have to be transmitted on to the hearing device. This type of simple control device is as a rule correspondingly small so that it can be worn directly on the body. To achieve a greater freedom of movement for the hearing aid wearer during a programming session, the control device can in this case be connected wirelessly to the adaptation computer instead of via cables.
With newer designs of programming system the control data for the programming of the hearing device can already be transmitted using wireless data transmission from the control device to the hearing device. Use is made of a wireless interface already integrated into the hearing device for this purpose. Audio signals also continue to be transmitted however by means of a special cable connection. With this type of transmission a cable must be directly accommodated on the hearing device. The freedom of movement of the hearing device wearer is restricted by the cable however. In addition a cable pulling on the hearing device can change the seating of the hearing device and thus also change the hearing impression, which can have a negative effect on the hearing device adaptation.
Finally analog modulated radio systems are also known with which audio signals from external sources can be coupled wirelessly into the hearing device. These devices embodied as external radio modules are plugged into an audio shoe of the hearing device. They use VHF frequencies and have a separate power supply. However a specific radio module is needed for each hearing device, since hearing devices vary from manufacturer to manufacturer. Furthermore radio modules plugged into the hearing device can also change the seating of the hearing device which can also have a negative effect on the hearing device adaptation.